Semiconducting SmS

In some sense this is similar to a uniaxial stress applied to the bulk crystal. For the semiconducting SmS (100) surface such surface relaxation, if large enough, is expected to have drastic influence on the electronic structure of the Sm ions, because the semiconductor-metal transition occurs when the bulk lattice constant has been... 

Fig. 70. LA phonon dispersion curves for the [111] direction for metallic (VF) and semiconducting SmS (Mook et al. 1982).

Fig. 131. Phonon spectra (a) of semiconducting SmS and L (b) of Smo.75Yo.25 (Mook and Holtzberg 1981, Mook and Nicklow 1978, Kikoin and Mishchenko 1988).

In fig. 10 we show a BIS spectrum for divalent, semiconducting SmS (Oh and Allen 1984). The BIS spectrum of divalent Sm should be analogous to that of trivalent Eu (4f initial-state configuration). The agreement with calculated f - f multiplet spectra is however poor, and more work is needed to establish experimentally whether all the features seen in the spectrum are 4f related. Oxidation yields Sm2 03 (trivalent Sm). The shape of the BIS spectrum of oxidized SmS is again only in fair agreement with that of trivalent Sm metal. 

Fig. 10. BIS spectra for semiconducting SmS which, upon oxidation, forms a trivalent Sm oxide, Sm Oj (Oh and Allen 1984).

Fig. 27. Energy level diagram of EuS and semiconducting SmS. (After Kaldis and Wachter 1972.)...

Fig. 28. Reflectivity of semiconducting SmS. The solid curve is after Batlogg et al. (1976b), the dashed curve after Gtlntherodt et al. (1983).

Fig. 31. Real and imaginary parts of the dielectric function of semiconducting SmS. The final state multiplets and the crystal-field splitting aru indicated. (After Batlogg et al. 1976b.)...

Fig. 38. Phonon dispersion relation of semiconducting SmS at 300 K. The abscissa is in fee reciprocal lattice units 2nla. (After Birgeneau and Shapiro 1977.)...

Fig. 39. Magnetic susceptibility of the semiconducting Sm monochalcogenides. Dashed lines represent the calculation according to van VIeck theory. (After Bucher et al. 1971.)...

Lattice-related properties. The phonon dispersion of Y-substituted Smo.75Yo.25S and high-pressure IV SmS has been measured with inelastic neutron scattering by Mook et al. (1978, 1982) and Mook and Holtzberg (1981) it is shown in fig. 54 for the three principal directions. The Sm used was isotopically pure Sm. Figure 54 should be compared with fig. 38 where the phonon dispersion of semiconducting SmS is shown and also with fig. 23 which is the phonon dispersion of IV SmBe. 

The ground state of Sm " in the Sm monochalcogenides is 4f ( F = 0,1,.. . , 6), with a 0.6 eV wide spin-orbit-split multiplet. Electronic Raman scattering from the different /-multiplet levels of cleaved (100) faces of semiconducting SmSe (Guntherodt et al. 1981a) is shown in fig. 2. The odd-/ levels show up for perpendicular incident ( ,) and scattered (Ej polarization vectors, where-... 

In the temperature region 1(T < Tc), the resistivity of PTC thermistor is in the range of 10-10 cm. To produce semiconductive BaTiOs, a small amount of rare earth metal ions (e.g. Sm + or La +) are substituted at the Ba + site, or Nb and Ta " " ions are substituted at the Ti site. These ions provide conductive electrons as shown in the following equations, using the defect notation of Kroger and Vink. 

Fig. 27. Formally constructed stability diagram for the lanthanide monosulphides. The diagram is obtained from the Fermi level referenced data for the semiconducting compounds SmS, EuS and YbS (Mirtensson et al. 1982b). Complications due to the non-metallic character of the divalent monosulphides, as for instance incomplete screening, are discussed in the text ...

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